Self-synchronizing tap driver for rigid tapping

ABSTRACT

Disclosed is a tap driver for rigid tapping, which includes predetermined tension and compression factors to self-synchronize the tap driver. In the preferred embodiment, the tap driver includes helical coils imparted in the tap driver body which allow the attachment body to synchronize axially in response to a force of a predetermined magnitude imparted on the tap. An additional embodiment of this invention provides such a tap driver body wherein the body allows for lateral flexure and movement to compensate for feed error and location error.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part of U.S. patent applicationSer. No. 09/629,490 now U.S. Pat. No. 6,348,003 which was filed on Jul.31, 2000 and which is incorporated by reference herein.

TECHNICAL FIELD

This invention pertains to a self-synchronizing and self-adjusting tapdriver for rigid tapping.

BACKGROUND OF THE INVENTION

In machining metallic work pieces, an apparatus called a tap is used tocreate internally threaded holes for receiving screws in the metallicwork pieces. The tap itself is a tool with external cutting threads. Inorder to create the internally threaded hole in the work piece, the tapis rotated and driven into the work piece to the desired hole depth, andthen reverse rotated and retracted from the work piece.

The tap is held by a tap driver, and the tap driver is held or securedwithin a machine which provides the forward and reverse rotation as wellas the forward and reverse drive.

In creating the internally threaded hole, the tap driver is firstrotated and driven into the base material or metal to the desired depth.Once the tap reaches the desired depth, the rotation of the tap driverand the tap is reversed and the tap is retracted from the base material.

In order to create the best internally threaded hole, the tap should besimultaneously advanced and rotated at precisely correlated rates ofrotation and forward movement for a given tap pitch. By way of example,a one-quarter-twenty tap should be advanced into the work piece one inchfor every twenty revolutions, or 0.05 inch for each revolution. Intypical rigid tapping, the driver machines provide the synchronizationof the spindle rotation and feed advance to match the tap pitch.

During the creation of a tap hole, the machine spindle goes throughseveral stages, namely driving the rotating tap into the tap hole,slowing the forward drive or feed rate and the rotation until the tapcomes to a stop in the work piece, reversing the direction of therotation and accelerating or increasing the reverse rate of rotation tomatch the desired tap pitch as the tap is retracted.

It is appreciated by those of ordinary skill in the art that during thechanges in rotation speed, the feed advance of the tap must be adjustedor correlated to precisely match the tap pitch. However, in practice itis very difficult to precisely match the rotation, drive and tap pitchand there are small errors that occur in the synchronization of therotation speed and the feed rate during the deceleration or slowing downphase, and during the reverse rotation acceleration phase.

In typical prior art, tapping drivers are generally solid in that theyhave no real ability to compensate for discrepancies between the feed ofthe tap and the feed advance of the machine, but instead merely directlytransfer the rotation and drive of the tapping machine.

With solid tap holders, even very small errors in the synchronizationwill apply a significant axial force on the tap, creating premature wearto the tap and negatively affecting the thread quality produced by thetap.

In machining numerous internally threaded apertures, one machine may beused to drill pilot holes into which the taps are driven, while adifferent machine may be used for the actual tapping. This may lead toslight positioning errors wherein the tap for instance is not exactlyaligned with the pilot hole, but instead may be one or two thousandthsof an inch off.

It will be appreciated by those of ordinary skill in the art that thereis a need for a tap driver which has some limited flexure for thelocation errors associated with locating the tap with respect to thedesired tap hole location.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is an elevation view of an embodiment of this invention showing atap driver with a tap device therein;

FIG. 2 is an elevation cross-sectional view of an embodiment of thisinvention showing a tap driver with a flexible area machined withhelical coils between the shank portion and the chuck portion;

FIG. 3 is an elevation view of a tap driver body which may be used in anembodiment of this invention;

FIG. 4 is an elevation cross-sectional view of the embodiment of theinvention shown in FIG. 1 but illustrating the compression flexure ofthe central portion of the tap driver body;

FIG. 5 is a top cross-sectional view of the embodiment of the inventionshown in FIG. 4;

FIG. 6 is an elevation view of an embodiment of the invention,illustrating lateral flexure provided by an embodiment of thisinvention;

FIG. 7 is an elevation view of another embodiment of a tap driver bodywhich may be used in connection with this invention;

FIG. 8 is an elevation partial view of another embodiment of a tapdriver body which may be used in an embodiment of this invention; and

FIG. 9 is an elevation cross-sectional view of an embodiment of thisinvention showing a tap driver with a flexible area machined withhelical coils between the shank portion and the chuck portion, andwherein the tap driver body is integral by being screwed together via athreaded joint.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Many of the fastening, connection, manufacturing and other means andcomponents utilized in this invention are widely known and used in thefield of the invention described, and their exact nature or type is notnecessary for an understanding and use of the invention by a personskilled in the art or science; therefore, they will not be discussed insignificant detail. Furthermore, the various components shown ordescribed herein for any specific application of this invention can bevaried or altered as anticipated by this invention and the practice of aspecific application or embodiment of any element may already be widelyknown or used in the art or by persons skilled in the art or science;therefore, each will not be discussed in significant detail.

The terms “a”, “an”, and “the” as used in the claims herein are used inconformance with long-standing claim drafting practice and not in alimiting way. Unless specifically set forth herein, the terms “a”, “an”,and “the” are not limited to one of such elements, but instead mean “atleast one”.

The tap driver provided by this invention may be used in combinationwith any one of a different machines or applications, with no one inparticular being required to practice this invention. It may be used forinstance in combination with a machining center which has rigid tappingcapability.

FIG. 1 is an elevation view of an embodiment of this invention showing atap driver attachment with a tap device therein, illustrating tappingattachment 1, tap driver body 2, shank portion 2 a of tap driver body 2,chuck portion 2 c of tap driver body 2, tap 40, collet nut 3, tap bodysleeve 4, and shank flat 30 to attach to a machine spindle or intoanother shank which fits into a machine spindle. The shank flat 30facilitates the securement of the tap driver to its source of rotationor ultimately to the machine spindle.

FIG. 2 is a cross-sectional elevation view of an embodiment of thisinvention which shows the tapping attachment 1, tap driver body 2, withtap driver body shank portion 2 a, tap driver body central portion 2 b,and tap driver body chuck section 2 c. In the central portion 2 b of thetap driver body 2, helical coils 5 have been cut into the body aroundthe circumference to provide a spring or tension and compressionproperties (and limited lateral flexure) different or dissimilar fromthat in the shank portion 2 a and chuck portion 2 c.

The helical coils can be precisely cut to provide the desired flexure,tension and compression necessary to allow the attachment body to selfsynchronize to forces imparted on the tap during tapping. Compressionoccurs by an upward force on the guide bushing 8 contained within tapdriver body axial aperture 11. When an excess force is incurred, it willbe transmitted through guide bushing 8 to first drive pin 6. First drivepin 6 then imparts or transfers said axial force to the helical coils 5in central portion 2 b to cause compression of the central portion 2 bof the tap driver body 2.

Compression gaps 17 provide space for, and limit, the movement of guidebushing 8 during compression of center portion 2 b. Compression gaps 17are shown larger than they actually would be for illustrative purposesonly. In a typical tapping attachment, the compression gaps may onlyneed to be one-half (½) of a millimeter in order to provide thesufficient movement for the desired synchronization.

The helical coils 5 may be cut into tap driver body 2 accurately andprecisely to create the desired spring characteristics to equate thecentral portion 2 b of tap driver body 2 to a thirty pound spring. Thehelical coils 5 may be machined into the central body portion by HelicalProducts, Inc. The extension and compression rate is approximatelyeleven hundred sixty seven (1167) pounds per inch reference, the springextension and compression of thirty one-thousandths inch maximum with areaction force of thirty five pounds, plus or minus ten percent. Thepreferred permitted lateral translation of spring is threeone-thousandths of an inch. The preferred material out of which thespring and/or tap driver body is constructed, is generally known as C300metal.

One embodiment of this tapping attachment is able to provide some slightlateral movement of the tap to the hole while still providing asufficiently accurate tap hole. The preferred embodiment of theinvention, through the helical groove portion, provides approximatelytwo one-thousandths ({fraction (2/1000)}) of an inch of movement side toside at the end of the tap to allow for slight mis-alignment of the tapwith the hole.

In a typical tapping application, the helical grooved area may providefor axial movement of up to thirty-one thousandths ({fraction(30/1000)}) of an inch, even though the typical axial movement will onlybe in the two-one thousandths ({fraction (2/1000)}) of an inch tofive-one thousandths ({fraction (5/1000)}) of an inch range. It ispreferred that there be approximately thirty-one thousandths ({fraction(30/1000)}) of an inch movement in response to approximately thirty (30)pounds of axial force, although the predetermined movement may be inresponse to any range of predetermined forces, all within thecontemplation of this invention.

Although there are embodiments of this invention in which are not onepiece or integral, it is preferred that the compression/tension area beintegral or one piece with the tap driver body for concentricity andother reasons. Utilizing an embodiment of this invention wherein the tapdriver body is one piece removes the reliance on the accurate assemblyor fitting of two pieces together.

FIG. 2 further illustrates tap driver body axial aperture 11 throughwhich cutting fluid or lubricant may be provided or routed for thetapping procedure. The guide bushing axial aperture 10 further providesthe necessary conduit for the coolant to reach the collet chuck 12 andbe provided to the tap hole during tapping, in accordance with knownmeans by those of ordinary skill in the industry.

FIG. 2 further illustrates second drive pin 9 spaced apart from tapdriver body 2 at least a distance equal to compression gap 17 to allowits movement. The first end 9 a of second drive pin 9 is in the at leastone drive pin aperture in the outer surface of the guide bushing 8 and asecond end 9 b of second drive pin 9 fits within aperture 20, which isbetter shown in FIG. 3 and is preferably oval shaped. Ball bearings 7are provided in gaps above and below the helical coils 5 to maintain thefirst drive pin 6 and the second drive pin 9 in their respectivelocations, while still allowing relative axial and lateral movement. Thefirst end 6 a of first drive pin 6 is in the at least one drive pinaperture in the outer surface of the guide bushing 8 and a second end 6b of first drive pin 6 is in the at least one drive pin aperture 21(better shown in FIG. 5) in the inner surface of the tap driver body 2.

O-rings 16 are shown between guide bushing 8 and tap driver body 2, theO-rings 16 providing a seal for containment and control of coolantinjected into tap driver body axial aperture 11.

The tapping attachment further includes tap body sleeve 4 whichgenerally surrounds the central portion 2 b of tap driver body 2. FIG. 2further shows collet nut 3 around the chuck portion 2 c of tap driverbody 2 for securing the tap into the chuck collet area 12. Also shown inFIG. 2 is shank flat 30 in the shank portion 2 a of tap driver body 2,and tap 40. FIG. 2 further shows sliding ring 33 and tap square 34.

The term central portion as used herein in reference to the tap driverbody is meant to include any area or portion of the tapping attachmentbetween where the tap driver is held by the tapping machine, and wherethe tap is held by the tap driver.

FIG. 3 is an elevation view of the tap driver body 2, illustrating theshank portion 2 a, central portion 2 b and chuck portion 2 c. Helicalcoils 5 are shown cut into central portion 2 b and surrounded by firstdrive pin aperture 21 and second drive pin aperture 20. It will be notedthat first drive pin aperture 21 provides a tight fit for first drivepin 6 to provide little or no relative movement between first drive pin6 and tap driver body 2. On the other hand, second drive pin aperture 20is intentionally larger than second drive pin 9 to allow for somerelative movement, as is more fully illustrated in FIG. 2. Collet nut 3is also shown around the chuck portion 2 c of tap driver body 2.

FIG. 4 is the same embodiment of the invention and view as shown in FIG.2, with each item and element being identically numbered. FIG. 4illustrates the axial or compression movement in the central portion 2 bof the tap driver body 2 when forces are exerted on the tap driver body2. FIG. 4 shows the helical portion being compressed and the compressiongap 17 being fully closed (there is no gap in FIG. 4 as compared to FIG.2).

FIG. 5 is a top cross-sectional view of a tapping attachment 1contemplated in one embodiment of the invention, illustrating threefirst drive pins 6 as preferably offset one hundred twenty degrees fromone another, ball bearings 7, central portion 2 b of tapping attachment2, tap body sleeve 4, guide bushing 8 and guide bushing axial aperture10.

It will be appreciated by those of ordinary skill in the art thatvariations of three drive pins 6 and spacing or offsetting between drivepins 6 may be varied into any one of a number of differentconfigurations and actual numbers of drive pins 6, all within thecontemplation of this invention.

FIG. 6 is an elevation view of a tapping attachment 1 contemplated inone embodiment of the invention, and illustrates lateral flexureprovided by an embodiment of this invention.

FIG. 6 shows tapping attachment 1, tap driver body 2, shank portion 2 aof tap driver body 2, chuck portion 2 c of tap driver body 2, tap 40,collet nut 3, tap body sleeve 4, and shank flat 30.

FIG. 6 further illustrates a slight lateral movement of the lower end ofthe tap 70, by a distance 71. The lateral movement of the lower end oftap 70 is generally provided by the central portion 2 c of the tapdriver body 2 and the grooves provided therein.

Distance 71 in FIG. 6 is exaggerated for illustration purposes, butgenerally may be one or two one-thousandths of an inch, which isgenerally an acceptable tolerance when machining tap holes. There may bea number of reasons this lateral flexure is needed. One example is ifone machine is used to drill the tap start holes and a second machine isused to actually tap the whole, there may be some slight variances inthe relative location of the intended drill holes versus tap hole.

FIG. 7 is an elevation view of another embodiment of a tap driver body 2which may be used in connection with this invention, illustrating ahoneycomb area 79 which provides the predetermined compression andtension for absorbing and providing axial forces, and which would alsoprovide for a lateral flexure. The honeycomb or matrix configurationincludes a plurality of first framework segments 80 and a plurality ofsecond framework segments 81. The matrix area 79 may be calibrated toprovide the desired predetermined axial compression and tension, as wellas the predetermined lateral flexure.

FIG. 8 is an elevation partial view of a tap driver body 2, a shankportion 2 a, and a shank flat 30. FIG. 8 illustrates another embodimentof this invention which provides the axial tension and compression,along with some lateral flexure.

FIG. 8 illustrates a dual flange area separated by a structure whichprovides the predetermined compression and tension for absorbing andproviding the axial forces. First flange 74 is attached to shank portion2 a of the tap driver body 2, and second flange 73 is attached to thechuck portion of the tap driver body 2, with O-ring 75 sandwichedbetween the two. Tension pegs 76 provide rotational stability betweenthe flanges and are attached to the first flange 74 and to the secondflange 73. The tension pegs 76 have a predetermined spring tensionfactor which provides the desired axial tension flexure and the o-ring75 provides the desired axial compression flexure. Any number of tensionpegs 76 may be used within the contemplation of the invention.

FIG. 9 is an elevation cross-sectional view of an embodiment of thisinvention showing a tap driver with a flexible area machined withhelical coils between the shank portion and the chuck portion, andwherein the tap driver body is integral by being screwed together via athreaded joint. FIG. 9 illustrates all the same components as from FIG.2, with the variation that it specifically shown an embodiment in whichthe tap driver body is attached together so that it is integral, but isattached together by screwing the two portions or sections together.FIG. 9 shows mating threads 100 between the central body portion of andthe shank portion, which operatively attach the two portions of the bodytogether, as well as interface 101 between the respective portions ofthe tap driver body operatively attached together.

Constructing the tap driver body together in such a way allows differentmaterials to be utilized for the compressible or central section, versusthe shank and/or chuck portions. Economies can be achieved if thematerials vary in cost, as well as other physical property benefits froma variation in material properties from one portion to another.

An embodiment of the invention therefore comprises a tap driver forrigid tapping, with a tap driver body comprising: a shank portion at afirst end of the tap driver body, the shank portion configured to besecured to a tapping machine; a chuck portion at a second end of the tapdriver; and a central body portion between the shank portion and thechuck portion, the central body portion having a predetermined axialcompressibility in response to axial forces imparted on the tap driverduring tapping.

In another embodiment of the invention, the central body portion betweenthe shank portion and the chuck portion includes helical spring coils,the helical spring coils having a pre-determined compressibility forabsorbing axial forces.

In yet another embodiment of the invention, the helical coils have apredetermined axial tension which allows a predetermined amount ofexpansion in response to axial tension forces imparted on the tap driverduring tapping, in combination with the pre-determined compressibilityand alone. In a further embodiment of the invention, the helical coilsprovide a predetermined lateral flexure in response to lateral forcesimparted on the tap driver during tapping, to allow the tap itself toadapt or move slightly in the lateral direction, to create a tap hole.

In a process embodiment of the invention, a process for making a tapdriver body for rigid tapping is provided, the process generallycomprising the steps of providing a tap driver body comprising, the tapdriver body comprising: a shank portion at a first end of the tap driverbody, the shank portion configured to be secured to a tapping machine; achuck portion at a second end of the tap driver; and a central bodyportion between the shank portion and the chuck portion; and machining ahelical coil into the central body portion, the helical coil having apredetermined compressibility or expandibility.

During the tapping procedure, as the tap is driven into or out of thebase material, typically metal, additional forces are placed on the tapwhich places the tap out of the desired synchronization. The centralportion of the tap driver provided by this invention provides acompressibility and an expansion factor, which help compensate for theseforces and provides the desired synchronization in tension and incompression.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A tap driver for rigid tapping, comprising: (a) a tapdriver body comprising: (i) a shank portion at a first end of the tapdriver body, the shank portion configured to be secured to a tappingmachine, and further having shank threads thereon (ii) a chuck portionat a second end of the tap driver; and (iii) a central body portionbetween the shank portion and the chuck portion, the central bodyportion having a predetermined axial compressibility in response toforces imparted on the tap driver during tapping, and further includingcentral body threads corresponding to the shank threads and disposedsuch that the shank portion may be operatively attached to the centralbody with the shank threads and the central body threads.
 2. A tapdriver for rigid tapping as recited in claim 1, and further wherein thecentral body portion has a predetermined axial expandability in responseto forces imparted on the tap driver during tapping.
 3. A tap driver forrigid tapping as recited in claim 2, and further wherein the centralbody portion has a predetermined lateral flexure in response to lateralforces imparted on the tap driver during tapping.
 4. A tap driver forrigid tapping as recited in claim 1, and wherein the predetermined axialcompressibility in the central body portion is provided by helical coilsin the central body portion.
 5. A tap driver for rigid tapping,comprising: (a) a tap driver body comprising: (i) a shank portion at afirst end of the tap driver body, the shank portion configured to besecured to a tapping machine, and further having shank threads thereon;(ii) a chuck portion at a second end of the tap driver; and (iii) acentral body portion between the shank portion and the chuck portion,the central body portion including helical spring coils, the helicalspring coils having a pre-determined compressibility for absorbingforces, and further including central body threads corresponding to theshank threads and disposed such that the shank portion may beoperatively attached to the central body with the shank threads and thecentral body threads.
 6. A tap driver for rigid tapping as recited inclaim 5, wherein the helical coils have a predetermined axial tensionwhich allows a predetermined amount of expansion in response to axialforces imparted on the tap driver during tapping.
 7. A tap driver forrigid tapping as recited in claim 6, and further wherein the helicalcoils provide a predetermined lateral flexure in response to lateralforces imparted on the tap driver during tapping.
 8. A tap driver forrigid tapping, comprising: (a) a tap driver body with an outer surfaceand an axial inner aperture with an inner surface, the tap driver bodycomprising: (i) a shank portion at a first end of the tap driver body,the shank portion configured to be secured to a tapping machine, andfurther having shank threads thereon; (ii) a chuck portion at a secondend of the tap driver; (iii) a central body portion between the shankportion and the chuck portion, the central body portion includinghelical spring coils, the helical spring coils having a pre-determinedcompressibility and a predetermined expandability for absorbing axialforces, and further including central body threads corresponding to theshank threads and disposed such that the shank portion may beoperatively attached to the central body with the shank threads and thecentral body threads; (iv) at least one drive pin aperture in the innersurface of the axial inner aperture of the tap driver body between thechuck portion and the helical coils; (b) a guide bushing comprising: (i)an outer surface which corresponds to the inner surface of the axialinner aperture of the tap driver body; (ii) a first bushing end and asecond bushing end, the second bushing end being disposed to receiveaxial forces from a tap; (iii) at least one drive pin aperture in theouter surface of the guide bushing, said at least one drive pin aperturecorresponding to the at least one drive pin aperture in the innersurface of the axial inner aperture of the tap driver body; and (c) adrive pin with a first end in the at least one drive pin aperture in theouter surface of the guide bushing and with a second end in the at leastone drive pin aperture in the inner surface of the axial inner apertureof the tap driver body.
 9. A tap driver for rigid tapping as recited inclaim 8, and further wherein the helical coils provide a predeterminedlateral flexure in response to lateral forces imparted on the tap driverduring tapping.
 10. A process for making a tap driver body for rigidtapping, comprising the following steps: (a) providing a tap driver bodycomprising: (i) a shank portion at a first end of the tap driver body,the shank portion configured to be secured to a tapping machine, andfurther having shank threads thereon; (ii) a chuck portion at a secondend of the tap driver; and (iii) a central body portion between theshank portion and the chuck portion, and further including central bodythreads corresponding to the shank threads and disposed such that theshank portion may be operatively attached to the central body with theshank threads and the central body threads; and (b) machining a helicalcoil into the central body portion, the helical coil having apredetermined compressibility or expandibility.